Regulator rheostat



Feb. 22, 1938. E 1 HARDER 2,109,214

REGULATOR RHEosTAT Filed Dec. 13, 19:55 2 sheets-sheet 1 wlNEssEs: INVENTO'R Harder.

Patented Feb. 22 1938Vv PATENT ori-ICE REGULATOR nnEoSTA'r Edwin n Harder, Pittsburgh, Pa, minor to Westinghouse Electric Manufacturing Commuy, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 13, 1935, Serial No. 54,256

'iClaiml- My invention relates to rheostats for electrica.1 regulating systems and other comparable applications and it has particular relation to means for increasing the number of steps of resistance adiustment which rheostats having a given number of stationary contact buttons are capable of providing.

Generally stated, the object of my invention is to increase the neness of resistance adjustment of face-plate type rheostats.

Another object is to provide a rheostat which without the aidof an external Vernier device offers resistance adiustment in steps much smaller than those determined by the resistance connected between the stationary contacts over which the adjusting arm traveln An additional object is to provide a rheostat of the above-described character in which the magnitude of the Vernier steps corresponds at any point in the range of rheostat adjustment to the graduation at that point of the tapering major steps of resistance. l

A further object is to provide a rheostat for use in electrical regulating systems which, when operated by a reversible motor, aii'ords a local range of ne adjustment steps, in addition to the usual broad range of coarser steps.

My invention itself together with additional objects and advantages lthereof will best be understood through the. following description of specific embodiments when taken in conjunction with the accompanying drawings, in which:

Figure 1 is a diagrammatic view of apparatus and circuits illustrating a regulating system in which the rheostats of my invention may with advantage be incorporated;

- Fig. 21s an enlarged view of the improved rheostat which forms a part .of thesystem 0f Fig. 1;

Fig. 3 is a representation of the circuits comprised by the rheostat of Figs. 1 and 2 simplied to illustrate the manner in which .vernier adjustments are obtained;

Fig. 4 is a more complete representation of one preferred mechanical arrangement of the stationary face-plate contact members' and the coop-y erating movable contacting assemblies actuated thereover by the rheostat operating arm; and Figs. 5, 6, and '7.-are comparable representations of a rheostat constructed in Aaccordance with a second embodiment of my invention in which the number of resistance steps obtainable with a given number of stationary contact buttons is doubled.

Since my invention has particular, although not exclusive, application to rheostats for use in `electrical regulating systems, I have chosen to explain it in connection with a system of this character. Such a rheostatic-type of regulating system is illustrated in Fig. l as being adapted to maintain constant the voltage of an alternatingcurrent circuit I0 which is supplied from a generator I2. The iield winding I4 of the generator is energized by an exciter I6 the field winding I8 of which derives energizing current from any suitable source of direct-current potential, shown in the form of a pilot exciter 20.

For the purpose of adjusting the magnitude o! this current to thereby control the voltage of generator I2, a rheostat 22, to which the iineness increasing expedients of my invention later vto be described may be applied, is connected in the manner shown in the energizing circuit of the exciter eld winding. Operation of this rheostat iseiected in well known manner by a motor 24, which is controlled through a'pair of relays 26 and 2l by means of a contact-making device 30 so connected as to be sensitive to changes in the voltage of the regulated circuit I0.

When, for example, this voltage falls below the desired value, the device 3,0 completes, through contact members 32 and R, an actuating circuit which causes relay 26 to so effect energization of motor 24 that it operates the rheostat 22 in a direction which lowers its eective resistance to thereby correctively raise the voltage of genervrheostat 22 in the opposite or generator-voltage lowering direction.

The system illustrated also includes a well known quick-response expedient comprising a pair oi' field forcing contactors 34 and 36 controlled by an auxiliary set of contact members L', 38 and R which respond only to excessively large errors in the regulated voltage. An excessively large drop in regulated voltage thus actuates contactor 36 to establish a shunting connection around the rheostat 22 and thereby rapidly raise the generator excitation while an excessively large rise in the regulated voltage similarly actuates contacter 34 to insert in the exciter field winding circuit a block of resistance 40 which rapidly reduces `the generator excitation.

The illustrated equipment also includes a calibration-changing or voltage-adjusting rheostat 42 and a pair of anti-hunting resistors 43 and 44 connected in the manner shown in the energizing circuit of the contact making device 30.

In the illustrated and in many other comparable applications, the necessity for ilne adjustment in the current controlled by the rheostat 22 requires that the resistance variation be eiected in a large number of relatively small steps. Rheostats for this service conventionally comprise, as is indicated in a simplified manner in Fig. 4, a plurality of stationary contact buttons 46, which are mounted on a face-plate of insulating material (not shown), and between which sections of the rheostat resistor are connected in the manner illustrated. The number of these sections included in the current-carrying circuit, which extends from one end D of -the resistor assemblage to point E, is determined by the position along the line of stationary contact buttons 46 of a cooperating movable contact member B which forms a part of the adjusting arm mechanism 48. This mechanism is actuated by the rheostat operating motor 24. y

In past constructions, the number of steps of resistance has been limited by the number of stationary contacts 46 with which the rheostat is provided. In many instances, of which the regulating system of Fig. 1 is but one, it is desirable to obtain a fineness of adjustment much greaterV than the largest number of stationary contact members 46 which it is feasible, for mechanical reasons, to provide on the rheostat face-plate. 'I'he stated limitation is occasioned by the fact 'that an increase in the number of contact buttons necessitates a larger radius of the button circle and this frequently means prohibitively large dimensions of the rheostat face-plate. In addition it makes impossible use of a standard line of equipment for applications ordinarily beyond its range.

A need, therefore, exists for means for increasing the number of effective steps of resistance adjustment without raising the number of stationary contact buttons. 'I'he expedients of my invention now to be explained satisfy this need in an exceedingly simple, inexpensive and satisfactory manner.

In accordance with the embodiment of my invention illustrated in Figs. 1 to 4, inclusive, I obtain the desired increase in adjustment flneness by supplementing the conventional single movable contact member B by an additional pair of movable members A and C. Member C is rigidly fixed to the rheostat actuating arm fixture 50 to which adjusting movements of the motor 24 or other operating means are directly communicated. Members A and B, on the other hand, are.

carried by a oating member 52, shown in the form of a block of insulating material, to which adjusting movements are transmitted only when the limits of a small range of independent travel of contact member C have been exceeded. Y

That is, contacts A and B supported from member 52 remain stationary until contact C has been moved in either direction by a distance sufiicient to bring the one or the other of the two opposing surfaces of the movement producing member 50 into engagement with an end of the member 52. Further movement, of course, results in a simultaneous shifting of all three of the contacts A, B, and C. If desired, adjusting screws 59 may be employed to change the magnitude of the local range of single contact adjustment.

Within the mentioned intermediate or local range of adjustment through which contact C only is moved, a Vernier adjusting effect is produced, as will be more clearly seen by an inspection of the simplified rheostat circuit representation of Fig. 3. The portion 54 of the rheostat resistor which is spanned by the two fixedly spaced contacts A and B is at all times paralleled by the portion 56 of the resistor which is spanned by contacts B and C.

The adjustment of this latter portion which the independent movements of contact C produce results in a much ner adjustment of the resistance between points A and E than is determined by the resistance connected between adjacent stationary contact buttons 46 (Fig. 4) over which contact C is moved. In consequence, there is provided a Vernier adjustment which very effectively solves the problem previously stated.

The cost of providing the additional contacts A and C and mounting them in the manner described on the rheostat adjusting arm is relatively slight. The increase in iineness of adjustment obtainable by a proper choice of the spacing between contact members A and B and the range of independent movement of member C may be made exceedingly great. A further advantage lies in the automatic coordination between the magnitude of the steps of Vernier adjustment to the gradation or taper of the major steps of the rheostat resistance at all points throughout the range of adjusting-arm travel.

This combination with the absence of additional or auxiliary rheostats or resistors of the above-named conforming of the Vernier steps to the taper of the major steps of the rheostat is of special importance in the described type of regulator rheostat which preferably must be so designed that each major step produces substantially the same change in current supplied to the exciter or other field winding (I8) through the circuit of which the rheostat (22) forms a part. To effect this result, it is necessary that the sections of the resistor represented at the right end of Fig. 4 be many times as large as those repres ted at the left end.

In a 20D-step rheostat, for example, the ohms per step may vary within a range of 50:1 from one end of the rheostat to the other. Obviously, any external vernier is either subject to too iine steps in one zone and to too coarse in another, unless, of course, considerable complication is resorted to to avoid this difficulty. In the expedient of my invention just described the vernier steps are in magnitude determined by the magnitude of the major steps at the particular point in the range of arm travel Within which operation takes place. It accordingly overcomes the abovenamed difficulty in a most satisfactory manner.

As applied to a rheostatic type of regulating system, such as is illustrated in Fig. 1, it has the further advantage that while considerable motion of the rheostat motor 24 and the arm member 50 in a local range shifts the position of contact member C only to thereby produce fine steps of resistance adjustment, still when a voltage change larger than that corresponding to this local range is required, the same speed of the rheostat motor quickly brings the xedly spaced contact members A and B to a new position in which the Vernier adjustments produced by independent movements of contact C may again be availed of.

In Figs. 5 to 7, I have illustrated a second embodiment of my invention which doubles the effective number of steps available for a given number of stationary or rheostat face-plate contact buttons. Cooperating with these buttons are a plurality of movable contact members 60, 62, 64 which are interconnected in the main circuit of the rheostat, shown as extending from bodiment.

The spacing, however, of these movable members relative to each other is always fixed and it,

together with their dimensions relative toI the stationary contact buttons over which they move, is also chosen in the manner indicated. That is, the spacing between the edges of members 60 and 62 is one half of 'the width of each of the stationary contact buttons. That between members 62 and 6l is a full button width; Members 60 and 64 are each two button pitches in width while the span of member. 62 is somewhat less than that of twofofA the adjacent of the stationary contact buttons. f

When the vmovable assemblage occupies the position shown in Fig. 5, the circuit from D' to E' includes the resistor section 66, shown as having a value of 10 ohms, stationary contact button 68, movable contact member 60, stationary button 10, and movable member 62, to which point E' is directly joined. For this condition, the resistance between points D' and E is 10 ohms.

Adjustment to the right oi' the movable assemblage to the position shown in Fig. 6 increases this resistance by only one-half of the value of each of the sections, shown as being 1 ohm each, of resistance connected between adjacent of the stationary contact buttons. 'Ihe circuit through the rheostat now includes resistor section 66 and sections 'I2 and 'M connected in parallel between stationary button 6l and movable button 62 through interconnected movable members 60 and 64 and stationary buttons 16 and 18 which the latter named members respectively contact. For

this position, the rheostat resistance is 10i/2 ohms.

Further adjustment to the right oi the movable assemblage to the position shown in Fig. '7 adds another l/2 ohm to the rheostat resistance. The current-carrying circuit now includes resistor sections 66 and 80 in series, and is completed through stationary button l2, movablecontact 60, stationary button Il, and movable contact 62. For this position. the rheostat resistance is 11 ohms.

Further movement to the right of the movable contact assemblage similarly raises the rheostat resistance in steps of a ohm each, even though the resistance between adjacent stationary contact buttons is 1 ohm. The described expedient thus doubles the number of resistance steps obtainable with a given number of stationary contact buttons.

-Although I have shown and described certain specic embodiments of my invention, I am fully aware that many modiiications thereof are possi'- ble. My invention, therefore, is not to be restricted, except insofar as is necessitated by the prior art and by the scope oi' the appended claims.

I claim as my invention:

l. In a rheostat comprising .a single tapped resistor, a plurality ot stationary contact buttons respectively connected with the resistor taps and spacedly arranged in a single row, and a member adapted to be moved in successive contact register with said buttons to thereby adjust the rheostat resistance, the combination of means for giving steps of adjustment substantially smaller than those determined by the resistor sections connected between adjacent oi said contact buttons comprising three button contacting elements spacedly carried by said movable member, the two outer of said button contacting elements being connected together and the center element serving to complete the main currentcarrying circuit through the rheostat, one of Said button contacting elements being connected to follow all movements of said member, the other two being spaced in fixed relation to each other and arranged to move in the one or the other direction only when the iirst element is so moved after reaching a limit of range of independent travel.

2. In a rheostat comprising a single tapped resistor, a plurality of stationary contact buttons respectively connected with the resistor taps and spacedly arranged in a single row, and a member adapted to be moved in successive contact register with said buttons to thereby adjust the rheostat resistance, the combination of means for givingk steps of adjustment substantially smaller than those determined by the resistor sections connected between adjacent of said contact buttons comprising three button contacting elements spacedly carried by said movable member in such manner that one directly follows all movements of said member while the other two, the spacing between which is maintained xed, have movement imparted thereto only when the first element reaches either limit of range of independent travel.

3. In a rheostat comprising a tapped resistor, a plurality of stationary contact buttons respectively connected with the resistor taps and arranged in spaced relation and a member adapted to be moved in successive contact register with said buttons to thereby adjust the rheostat resistance, the combination of means for giving steps of adjustment substantially smaller than those determined by the resistor sections connected between adjacent of said contact buttons comprising three contacting elements spacedly carried by said movable member in such manner that one directly follows all movements of said member while the other two, the spacing between which is maintained fixed, have movement imparted thereto only when the first element reaches either limit of a range of independent travel, said elements being so interconnected that the portion of rheostat resistor spanned by the two fixedly spaced elements is parallel connected with the adjustable portion further spanned by the element first referred to.

4. A rheostat comprising a single tapped resistor, a plurality of stationary contact buttons respectively connected with the resistor taps and spacedly arranged in a single row, an assemblage, including three spaced contacting elements, adapted to be moved in successive register with said buttons to thereby adjust the rheostat resistance, means for maintaining fixed the spacing between two of said elements, means for moving the third in direct accordance with the assemblage movements, means for imparting movement to the iixedly spaced elements only when the third reaches either limit of a range of independent travel. and means for so interconnecting said elements that said independent movement of the third produces steps of resistance adjustment which are substantially smaller than those determined by the resistor sections connected between adjacent of said stationary contact buttons.

5. A rheostat comprising a tapped resistor, a plurality oi' stationary contact buttons respectively connected with the resistor taps and arranged in spaced relation, an assemblage, including three spaced contacting elements, adapted to be moved in successive register with said buttons to thereby adjust the rheostat resistance, means ior maintaining iixed the spacing between two of said elements, means for moving the third indirect accordance with the assemblage movements, and means for imparting movement to the xedly spaced elements only when thethird reaches either limit of a range of independent travel, said elements being so interconnected that the portion of rheostat resistor spanned by the two nxedly spaced elements is parallel-connected with the adjustable portion further spanned by the third element, positional changes of the latter thereby producing smaller steps of resistance adjustment than those determined by the resistor sections connected between adjacent of said stationary contact buttons.

6. In a rheostat comprising a single tapped resistor, a plurality of stationary contact buttons respectively connected with the resistor taps and spacedly arranged in a single row, and a member adapted to be moved in successive contact register with said buttons to thereby adjust the rheostat resistance, the combination of means for giving steps of adjustment twice as small as those determined by the resistor sections connected between adjacent of said contact buttons comprising three contacting elements spacedly carried by said movable member and which in mechanical size and spacing are so related to the stationary contact buttons that when the movable member occupies positions of register intermediate adjacent of said buttons the rheostat current carrying circuit is completed in parallel through two or' the sections of resistor which are connected between contact buttons.

7. In a rheostat comprising a single tapped resistor, a plurality of stationary contactbuttons respectively connected with the resistor taps and spacedly arranged in a single row, and a member adapted to be moved in successive contact register with said buttons to thereby adjust the rheostat resistance, the combination of means for giving steps of adjustment twice as small as those determined by the resistor sections connected between adjacent of said contact buttons comprising three contacting elements spacedly carried by said movable member and which in mechanical size and spacing are so related to vthe stationary contact buttons that when the movable member occupies positions of register intermediate adjacent of said buttons the rheostat-current carrying circuit is completed in parailel through two of the sections of resistor which are connected between contact buttons, the two outer of said .elements being connected together and the center element serving to complete said` current-carrying circuit.

EDWIN' L. HARDER.. 

